Software Design and Application of Encoder VD5026 Using Single Chip Microcomputer

　　Each group of serial data output waveform of VD5026-4 consists of a synchronization pulse, a 12-bit encrypted address (and control data) and a 1-bit stop bit. The order of the coded pulse output is AO~A7, A8/DO~All/D3, and each group of serial data is output at least 4 times. After mastering the output format of the serial data and its data verification method, pulse period, pulse duty cycle and its corresponding data relationship, write an application according to the requirements of the coded pulse output to enable the microcontroller to realize the function of the encoder. The simulation encoder program flowchart is shown in the figure below.

　　The infrared remote control keyboard designed with this technology has been applied to the "color remote control monitoring system". The principle of the remote control keyboard is shown in the figure below.
　　
　　This circuit uses the single-chip microcomputer AT89C2051, which is a high-cost single-chip microcomputer. The device uses the 80C31 core, and the instruction system and pins are fully compatible with MCS-51TM. There is a 2 KB reprogrammable flash memory, which can be erased/written 1,000 times and the data can be saved for 10 years.
　　
　　The decoder VD5027 has a 4-bit data output and can translate 16 states to meet the requirements of a 3×4 keyboard.
　　
　　The single-chip microcomputer finds that when a key is pressed, it generates a coded pulse corresponding to this key value. The coded pulse signal is modulated with a 38 kHz pulse signal and transmitted through the transmitting tube (SE303A). The infrared receiving diode (PH302B) converts the received infrared signal into an electrical signal, which is amplified and detected by the infrared remote control receiver CX20106 and converted into a pulse electrical signal. After being shaped and amplified, the signal is restored to the coded pulse output corresponding to the key value and sent to the 14-pin DIN input terminal of the decoder VD5027.
　　
　　When VD5027 receives the first string of coded pulse signals, if it is exactly the same as the address set by VD5027, the transmitted DO-D3 four-bit data code is sent to the register (and the serial code is changed to parallel code). When the second string of the same coded pulse signal arrives, it is checked again. If the address is correct and the control data is consistent with the first one, the logic control circuit in VD5027 sends a control signal to enter the control data of the register into the latch and output it to the DO~D3 terminal of VD5027. At the same time, the TV terminal changes from low level to high level, indicating that the decoding is valid.
　　
　　After receiving the valid decoding signal, the host reads the output data DO~D3 from VD5027, decodes the key value code, and performs the corresponding operation.